The present invention relates to a range-finding method in which light pulses are sent to a remote target, and in which the round-trip transit time of a target-reflected light pulse is measured; the invention also relates to apparatus for carrying out this method.
Optoelectronic rangefinders, for example laser rangefinders, send out coherent light pulses which are target-reflected back to the rangefinder. The distance to the target is determined by measuring the elapsed time between transmission of the laser-light pulse and return of the target-reflected laser-light pulse to the receiving device of the laser rangefinder; the distance to the target is calculated by an associated electronic system. In accordance with the known state of the art, at least one counter is started upon the emission of a pulse of laser light in order to effect this calculation. This counter totalizes the number of time intervals which elapse until the arrival of a light pulse reflected by the target. The counter is stopped upon the arrival of the light pulse. In the event different targets give rise to range-finder reception of several reflected-light pulses for a given transmitted pulse, several counters which were started upon the emission of the light pulse can be stopped, one after the other. Such a method of measurement and an arrangement for carrying out the method are to be found in the publication, "Laser Handbook", Vol. 2, edited by F. T. Arecchi and E. O. Schulz-Dubois, North Holland Publishing Company, 1972, pages 1783-1787.
This known prior art has the disadvantage that use of conventional counter modules necessitates memory storage of intermediate counter values with the full resolution of the counter (for example, 16 bit). The transfer of the intermediate counter values into memory storage must then be effected within one cycle of the counter. Due to the high expense for circuitry, one generally dispenses with the possibility of storing all possible intermediate counter values and stores merely two or three counter values.